The keyboards now being used on the notebook computers generally include a membrane in addition to the button keys on the upper layer, base plate and frame. To make the membrane, a button key configuration layout has to be defined and formed first by the vendor. Then the layout definition is transferred to manufacturers to make a matrix configuration (as shown in FIG. 1). Each button key position has a code to be built into the chip.
The membrane is made according to the finished matrix configuration of the button key position set forth above. In the manufacturing processes of the membrane, first, the membrane PET is heated and pre-shrunk, then a circuit made from a silver paste is printed on the membrane, an insulation layer is printed on the silver paste printed circuit, then a cover layer is printed on the insulation layer, then silver paste of jumping line is printed on the cover plate, another insulation layer is printed on the jumping line and carbon powders are printed, finally the membrane is folded and welded by supersonic wave, and structural holes are punched to complete the membrane production.
Production of the membrane with jumping set forth involves many printing operations. Thus manufacturing processes are complex, production cost is higher, yield is lower, and defect rate is greater. In addition, the jumping portion generates a circuit ionization phenomenon and results in greater micro short circuit. The reliability of the product becomes lower. Moreover, the print position of jumping is prone to form uneven membrane thickness and affects key in operation.
Furthermore, when the keyboard made by the aforesaid method is in use, the microprocessor located inside the keyboard constantly scans the matrix to check whether the key has been pushed downwards. In the event that composite keys are depressed (i.e. the composite keys means three keys have been depressed simultaneously), the microprocessor scans the depressed composite keys and usually mistakenly deems a fourth key is also being depressed (as shown in FIG. 5). As a result, a ghost key signal is generated and an additional character appears in the character string on the display screen. It causes inconvenience to users.